Biased Ghrelin Receptor Signaling and the Dopaminergic System as Potential Targets for Metabolic and Psychological Symptoms of Anorexia Nervosa

Diagnosis and Treatment of Pediatric Feeding Disorders: A Narrative Literature Review

Background/Objectives: The definitions of feeding disorders of infants and young children were historically based on a dichotomic organic/non-organic vision. Since 2019, a new definition of pediatric feeding disorders (PFDs) has reshaped the understanding of these disorders with a global vision. The aim of this study is to obtain a better understanding of the diagnostic criteria for general practice, both by exploring the evolution of classifications and by clearing the actual definition of PFDs and their possible treatments. Methods: We conducted a narrative review of the literature, including 36 articles about PFDs, excluding adolescents, anorexia nervosa, bulimia, pica, rumination, and specific neurodevelopmental or chronic pediatric disorders. We summarized these studies in three parts: the specific classifications for children before puberty, the current definition, and the clinical guidelines. Results: Concerning the history of the classifications, we summarized the studies of Chatoor and Kerzner and the older pediatric vision of failure to thrive. For the definition of pediatric feeding disorders, we presented this new category involving at least one out of four domains: medical, nutritional, feeding skills, or psychosocial. For the main clinical guidelines, we presented recommendations for both severe and common PFDs in each altered domain for use in daily practice. Conclusions: The new definition promotes a transdisciplinary vision of childhood feeding disorders, which considers each of the intricate domains of PFDs. Using common terminology for PFDs could help all healthcare providers, families, and researchers to better understand and address PFDs.

G protein-coupled receptors: A golden key to the treasure-trove of neurodegenerative diseases

G protein-coupled receptors (GPCRs) are a class of transmembrane proteins that distribute in various organs extensively. They can regulate physiological functions such as perception, neurotransmission and endocrinology through the synergies of signaling pathways. At present, Food and Drug Administration (FDA) have approved more than 500 drugs targeting GPCRs to treat a variety of conditions, including neurological diseases, gastrointestinal diseases and tumors. Conformational diversity and dynamic changes make GPCRs a star target for the treatment of neurodegenerative diseases. Moreover, GPCRs can also open biased signaling pathways for G protein and β-arrestin, which has unique functional selectivity and the possibility of overcoming side effects. Some studies believe that biased drugs will be the mainstream direction of drug innovation in the future. To disclose the essential role and research process of GPCRs in neurodegenerative diseases, we firstly reviewed several pivotal GPCRs and their mediated signaling pathways in Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). Then we focused on the biased signaling pathway of GPCRs in these diseases. Finally, we updated the GPCR drugs under research for the treatment of neurodegenerative diseases in the clinical trials or approval. This review could provide valuable targets for precision therapy to cope with the dysfunction of neurodegenerative diseases in the future.

Modulation of Hypothalamic Dopamine Neuron Activity by Interaction Between Caloric State and Amphetamine in Zebrafish Larvae

Dopamine (DA) signaling is evoked by both food and drugs that humans come to abuse. Moreover, physiological state (e.g., hunger versus satiety) can modulate the response. However, there is great heterogeneity among DA neurons. Limited studies have been performed that could resolve the interaction between physiological state and drug responsivity across groups of DA neurons. Here, we measured the activity of neurons in transgenic Tg (th2:GCaMP7s) zebrafish larva that expresses a calcium indicator (GCaMP7s) in A11 (posterior tuberculum) and a part of A14 (caudal hypothalamus and intermediate hypothalamus) DA populations located in the hypothalamus of the larval zebrafish. Fish were recorded in one of two physiological states: ad-libitum fed (AL) and food deprived (FD) and before and after acute exposure to different doses of the stimulant drug amphetamine (0, 0.7, and 1.5 μM). We quantified fluorescence change, activity duration, peak rise/fall time, and latency in the calcium spikes of the DA neurons. Our results show that baseline DA neuron activity amplitude, spike duration, and correlation between inter- and intra-DA neurons were higher in the FD than in the AL state. Dose-dependent AMPH treatment further increased the intensity of these parameters in the neuron spikes but only in the FD state. The DA activity correlation relatively increased in AL state post-AMPH treatment. Given that hunger increases drug reactivity and the probability of relapse to drug seeking, the results support populations of DA neurons as potential critical mediators of the interaction between physiological state and drug reinforcement.

Dual pancreatic adrenergic and dopaminergic signaling as a therapeutic target of bromocriptine

Bromocriptine is approved as a diabetes therapy, yet its therapeutic mechanisms remain unclear. Though bromocriptine's actions have been mainly attributed to the stimulation of brain dopamine D2 receptors (D2R), bromocriptine also targets the pancreas. Here, we employ bromocriptine as a tool to elucidate the roles of catecholamine signaling in regulating pancreatic hormone secretion. In β-cells, bromocriptine acts on D2R and α2A-adrenergic receptor (α2A-AR) to reduce glucose-stimulated insulin secretion (GSIS). Moreover, in α-cells, bromocriptine acts via D2R to reduce glucagon secretion. α2A-AR activation by bromocriptine recruits an ensemble of G proteins with no β-arrestin2 recruitment. In contrast, D2R recruits G proteins and β-arrestin2 upon bromocriptine stimulation, demonstrating receptor-specific signaling. Docking studies reveal distinct bromocriptine binding to α2A-AR versus D2R, providing a structural basis for bromocriptine's dual actions on β-cell α2A-AR and D2R. Together, joint dopaminergic and adrenergic receptor actions on α-cell and β-cell hormone release provide a new therapeutic mechanism to improve dysglycemia.